Adding test for image detection

Tests/ImagyTest.php

@@ -76,4 +76,16 @@ class ImagyTest extends BaseTestCase
 
         $this->assertEquals($expected, $path);
     }
+
+    /** @test */
+    public function it_should_detect_an_image()
+    {
+        $jpg = $this->imagy->isImage('image.jpg');
+        $png = $this->imagy->isImage('image.jpg');
+        $pdf = $this->imagy->isImage('pdf.pdf');
+
+        $this->assertTrue($jpg);
+        $this->assertTrue($png);
+        $this->assertFalse($pdf);
+    }
 }